I used to live in Derby (20 minutes on the bus)- and Nottingham is a lot better (although the bus of Derby people would often pass busses of Nottingham people heading the the opposite direction).

Nottingham has- a pretty castle
the oldest pub in england (although another pub somewhere has challenged it, time team couldn't figure it out)
The Robin Hood experiance

Shit loads of night clubs/pubs/bars- if your into the alt scene then I could point the way to a few good biker/metal/goth places.
Lots of gigs happening all over the place, including some big venues.
Excellent shopping if your a musician or like clothes, or sex toys.

Two univerities so loads of student nights etc- and the highest female to male ratio is correct- try rock city on a thursday night (if thats still student night)

Excellent rail and bus connections if you want to escape to another city for the night.